Crosslinkable saturated and unsaturated carbosilane polymers and formulations

ABSTRACT

Crosslinkable saturated and unsaturated carbosilane polymers are prepared by polymerizing vinyl substituted 1-silacyclo-pent-3-ene or vinyl substituted 1-silacyclobutane monomers in the presence of an anionic ring opening catalyst.

This invention relates to crosslinkable saturated and unsaturatedcarbosilane polymers and formulations, as well as methods of making thesame.

BACKGROUND OF THE INVENTION

W. P. Weber and S. Q. Zhou in previous applications have claimedpoly(unsaturated carbosilane) polymers and copolymers containing silylhydride reactive groups in the polymer chain Ser. No. 636,639 filed Dec.29, 1990 and its continuation-in-part, Ser. No. 758,638, filed Sep. 9,1991. Also disclosed in those applications were prior art on thepreparation of poly(1,1 dimethyl-1-silapent-3-ene) andpoly(1,1-diphenyl-1-silapent-3-ene) by ring opening metathesispolymerization or anionic polymerization. The Weber and Zhouapplications claim novel unsaturated carbosilane polymers and copolymersformed by anionic or metathesis polymerization which proceedssurprisingly in the presence of silylhydride in the monomer. Thoseskilled in the art would expect the initiating anion to displace hydridefrom silicon and would thus prevent anionic polymerization. The ringopening metathesis polymerization was surprising because thesilylhydride does not reduce the tungsten catalyst and thepolymerization proceeds to high molecular weight.

In Isvestya Akademia Nauk no. 8, 1448-1453, (1965), Nametkin et aldisclose the preparation of insoluble crosslinked saturatedsilahydrocarbon polymers with pendant vinyl groups.

SUMMARY OF THE INVENTION

The present invention relates to novel vinyl bearing carbosilanepolymers and copolymers with saturated or unsaturated polymer chainsmade by anionic polymerization. It further relates to crosslinkingformulations of these polymers with silylhydride crosslinking agents andcatalysts for carrying out hydrosilation crosslinking reactions. Thepolymers of this invention are vinyl bearing silapentene and silabutanepolymers and their crosslinking formulations with aliphatic or aromaticsilylhydride compounds containing more than one .tbd.SiH group.

Also, a novel method for preparing the vinyl bearing carbosilanepolymers of the present invention has been discovered. Surprisingly, thepolymers can be prepared by anionic ring opening polymerization of vinylbearing silacyclopentenes or silacyclobutanes. This is surprising sinceall the prior art teaches that the vinyl group should either polymerizeanionically or form a relatively stable anion adjacent to the siliconatom in the monomer. (Buell G-R, et. al. (1970) J Am Chem Soc92:7424):(Rickle G-K (1986) J Macromol Sci Chem A23:1287.) Either ofthese reaction products would prevent the preparation of the polymers ofthis invention by anionic polymerization.

DESCRIPTION OF THE INVENTION

The substituted 1-silacyclo-pent-3-ene monomers of this invention arerepresented by the following general structural formula: ##STR1## whereR is vinyl, an alkyl radical containing from one to four carbon atoms orphenyl, R¹ is hydrogen, an alkyl radical containing from one to fourcarbon atoms, phenyl, or a halogen and R² is hydrogen, or R¹ and R²together with the two adjacent carbon atoms for each form a phenyl ring.

Representative silacyclopentene monomers include:1-vinyl-1-methyl-1-silacyclopent-3-ene,1-vinyl-1-phenyl-1-silacyclopent-3-ene,1,1-divinyl-1-silacyclopent-3-ene, 2-methyl-2-vinyl-2-silaindan,2-phenyl-2-vinyl-2-silaindan, and 2,2-divinyl-2-silaindan. Preferredmonomers are 1-vinyl-1-methyl-1-silacyclopent-3-ene and1-vinyl-1-phenyl-1-silacyclopent-3-ene.

The substituted 1-silacyclobutane monomers of this invention arerepresented by the following structural formula: ##STR2## where R isvinyl, an alkyl groups with from one to four carbon atoms or phenyl, R₁is hydrogen, an alkyl group with from one to four carbon atoms, phenyl,or a halogen, and R₃ is hydrogen, an alkyl group with from one to fourcarbon atoms or phenyl.

The ring opening polymerizations proceed readily at low temperaturese.g. from about -20° C. to about -78° C. and at ambient pressures toproduce polymers having repeating units of the structural formula:##STR3## where R, R₁, and R₂ are as defined above ##STR4## where R, R₁and R₃ are as defined above.

The ring opening polymerization in accordance with this invention iscarried out in the presence of known anionic ring-opening catalystsystems. Such catalyst systems include an organometallic base and cationcoordinating ligand, such as an alkyllithium and hexamethylphophoramide(HMPA) or N,N,N¹,N¹ -tetramethylethylenediamine (TMEDA) catalystsystems.

The alkyllithium catalysts are used in conjunction with cationcoordinating ligands, such as hexamethylphophoramide (HMPA), N,N,N¹,N¹-tetramethylethylenediamine (TMEDA), N,N¹ -dimethylpropyleneurea, in apolar solvent such as tetrahydrofuran (THF).

The silacyclopentene, silaindan, or silacyclobutane monomers may becopolymerized with each other or other silahydrocarbon rings to make awide variety of block or random copolymers, terpolymers, and so forth.Preferred co-monomers have dimethyl, diphenyl, or phenyl methylsubstituted silicon in the silahydrocarbon ring. A representative ofthis variety of copolymers can be prepared by copolymerization ofmonomers such as 1-phenyl-1-methyl-1-silacyclopent-3-ene and1-vinyl-1-phenyl-1-silacyclpent-3-ene as described in the examplespresented below.

Representative comonomers include 1,1-dimethyl-1-silacyclopent-3-ene,1,1-diphenyl-1-silacyclopent-3-ene, 1,1-diethyl-1-silacyclopent-3-ene,1,1,3-trimethyl-1-silacyclopent-3-ene,3-chloro-1,1-dimethyl-1-silacyclopent-3-ene,1-methyl-1-phenyl-1-silacyclopent-3-ene, 2,2-dimethyl-2-silaindan,2,2-diphenyl-2-silaindan, 2,2-diethyl-2-silaindan,2-methyl-2-phenyl-2-silaindan, 1,1-dimethyl-1-silacyclobutane,1-ethyl-1-phenyl-1-silacyclobutane, 1,1-diphenyl-1-silacyclobutane.Preferred comonomers include 1,1-dimethyl-1-silacyclopent-3-ene,1,1,3-trimethyl-1-silacyclopent-3-ene,3-chloro-1,1-dimethyl-1-silacyclopent-3-ene, and2,2-dimethyl-2-silaindan and 1,1-diethyl-1-silacyclobutane.

By varying the composition and relative amounts of the comonomers, it ispossible to select copolymer and crosslinker combinations which producea wide range of properties in the crosslinked polymer formulation.

The silylhydride crosslinking agents may be represented by the followinggeneral structural formula: ##STR5## where R is an aromatic or aliphaticradical, and R₁, R₂, R₃, R₄ are hydrogen, phenyl, or an alkyl radicalwith from one to four carbon atoms. Typical crosslinking agents are1,4-bis(dimethylsilyl)benzene, 1,1,4,4-tetramethylsilylethane, and1,10-dimethyl-1,10-disiladecane.

The hydrosilation crosslinking reaction is catalyzed by many Group VIIImetal compounds but predominate among these are platinum compounds.Suitable platinum complexes are formed from Speiers catalyst which ischloroplatinic acid dissolved in isopropyl alcohol and usually added at10^(-4-to-6) mole/mole reactant. Other useful soluble platinum-vinylsiloxane complexes are sold by Huls America under the productdesignation PC072 and PC075.

Various particulate, fibrous, or fabric fillers and reinforcements canbe processed with the polymer formulations of this invention to givelaminates or molded articles. Solutions of these polymer formulationsmay be used to facilitate coating substrates like fiberglass nonwovenmats or cloth. Such coatings on glass or metal substrates promoteadhesion, provide environmental protection, or impart the property ofselective permeability. Because of their low dielectric constant thepolymer formulations of this invention are useful matrix materials forprinted circuit boards.

The polymers can be modified or crosslinked to change their physical andchemical properties. The polymers can be modified by reacting thecarbon-carbon double bonds. Representative reactions of thecarbon-carbon double bonds are ionic and free radical additionreactions, such as addition of hydrobromic acid, catalytichydrogenation, hydroboration, and the like. The permeability of polymercoatings, for example, can be varied by adding halocarbon or silanegroups through addition reactions with the carbon-carbon double bond.The adhesiveness of such coatings can be increased by reacting polargroups, such as alkoxysilanes, to the carbon-carbon double bonds.

The presence of olefinic unsaturation provides convenient sites forsubsequent vulcanization or cross-linking by ionic, free radical orthermal means known to the art.

The examples below are included to illustrate the invention. They arenot limitations thereon.

NMR Spectroscopy: ¹ H, ¹³ C and ²⁹ Si NMR spectra were obtained eitheron an IBM Brucker 270-SY or a Brucker AM-360 spectrometer operating inthe Fourier transform mode. ¹³ C NMR spectra were run with broad bandproton decoupling. A heteronuclear gated decoupling pulse sequence witha pulse delay of 20 s(NONOE) was used to obtain ²⁹ Si NMR spectra. Tento fifteen percent solutions in CDCl₃ were used to obtain ¹³ C and ²⁹ Sispectra. Five percent solutions were used to obtain ¹ H NMR spectra. ²⁹Si NMR spectra were externally referenced to TMS.

UV Spectroscopy: UV spectra were recorded on a Shimadzu-260 UV visiblespectrometer. Spectra quality THF was used to prepare solutions for UVspectroscopy.

Gel permeation chromatography (GPC): The molecular weight distributionof the polymer was performed on a Waters system. This was comprised of aUGK injector, a 510 pump, a R401 differential refractometer and aMaximum 820 data station. A 7.8 mm×30 cm Waters Ultrastyragel linear gelcolumn packed with less than 10 μm particle size mixed pore sizecrosslinked styrene divinylbenzene copolymer maintained at 25° C. wasused for the analysis. The eluting solvent was HPLC grade THF at a flowrate of 0.6 mL/minute. The retention times were calibrated against atleast five appropriate known monodisperse polystyrene standards whoseM_(w) /M_(n) were less than 1.09.

Elemental Analysis: Elemental Analysis was performed by GalbraithLaboratories, Knoxville, Tenn.

THF was distilled from a blue solution of sodium benzophenone ketylimmediately prior to use. Hexamethylphosphoramide (HMPA) was distilledfrom calcium hydride and stored over a 4 Å molecular sieves. Hexane wasdistilled from LiAlH₄.

n-Butyllithium in hexane (2.5 mol 1⁻¹) (from Aldrich) were used asreceived. Dichloromethylsilane, dichlorophenylsilane, trichlorosilaneand other silanes (from Petrarch Systems) were purified by fractionaldistillation.

All reactions were carried out under an Argon atmosphere. All glasswarewas flame-dried immediately prior to use.

EXAMPLE 1 1-Methyl-1-Phenyl-1-Silacyclopent-3-ene

In a 500 mL two neck rb flask equipped with a reflux condenser, a Tefloncovered magnetic stirring bar and a rubber septum was placed activemagnesium powder (9.6 g, 0.4 mol), methylphenyldichlorosilane (38.2 g,0.2 mol) and THF (300 mL). The reflux condenser was connected to arefrigeration unit. Ethylene glycol cooled to -20° C. was circulatedthrough the reflux condenser. 1,3-Butadiene (15.1 g, 0.28 mol) wascondensed at -78° C. into a volumetric flask which was sealed with arubber septum. The 1,3-butadiene was transferred into the reaction via acannula. The reaction mixture was stirred at rt for 24 h. Ether (2×100mL) was added. The organic solution was decanted from the magnesiumchloride salts. These were transferred to a sintered glass funnel andwere washed with ether (100 mL). The combined organic solution waswashed with water (2×50 mL), dried over anhydrous magnesium sulfate,filtered and the volatile solvents removed by evaporation under reducedpressure. The residue was purified by distillation through a 10 cmvacuum jacketed Vigreux column. The expected compound, bp 105°-107° C.,5 mm Hg, 42% yield, was collected.

EXAMPLE 2 1-Phenyl-1-Vinyl-1-Silacyclopent-3-ene

1-Phenyl-1-vinyl-1-silacyclopent-3-ene was prepared by the reaction ofphenylvinyldichorosilane, 1,3-butadiene, and magnesium in THF as inexample 1. Spectral properties ¹ H NMR δ:1.70(s,4H), 5.92(d,d,1H,J=20Hz, 3.8 Hz), 6.01(s,2H), 6.17(d,d,1H,J=14.7 Hz, J=3.8 Hz),6.46(d,d,1H,J=20 Hz, J=14.7 Hz), 7.40 (m,3H), 7.62 (m,2H). ¹³ C NMRδ:16.09, 127.87, 129.38, 130.84, 134.26, 134.62, 134.75, 136.00. ²⁹ SiNMR δ:4.69.

EXAMPLE 3 1,1-Divinyl-1-Silacyclopent-3-ene

In a 1 L three neck flask equipped with a Teflon covered magneticstirring bar, reflux condenser and a pressure equalizing additionfunnel. Vinyl magnesium bromide (0.5 mol) in THF 350 mL was placed inthe reaction flask. The flask and its contents were cooled to 0° C. inan ice water bath. 1,1-Dichloro-1-silacyclopent-3-ene (Damrauer, R.;Simon, R.; Laporterie, A.; Manuel, G.; Park, Y. T.; Weber, W. P. J.Organomet. Chem., 1990, 391, 7) (11 g, 72 mmol) dissolved in 20 mL ofTHF was placed in the addition funnel and was added dropwise to reactionflask. The reaction was allowed to slowly warm to room temperature over6 hours. The reaction mixture was poured into ice cold solution ofsaturated aqueous ammonium chloride. Ether (200 mL) was added and theorganic layer was washed with an equal volume of water (3×). The organiclayer was dried over anhydrous calcium chloride, filtered and thevolatile organic solvents were removed by distillation through a 15 cmvacuum jacketed Bigreux column at atmospheric pressure. The product wasdistilled under reduced pressure. A fraction bp 43°-45° C./16 mm Hg, 9.4g, 95% yield was obtained. ¹ H NMR: 1.44(d,4H, J=1 Hz), 5.87(t,2H, J=1Hz), 5.81(dd,2H, J=20 and 3.9 Hz), 6.06(dd,2H, J=14.5 and 3.9 Hz),6.22(dd,2H, J=20 and 14.5 Hz). ¹³ C NMR: 15.46, 130.71, 134.00, 135.02.²⁹ Si NMR: 1.56. IR: 3040, 3020, 2940, 2885, 1605, 1400, 1200, 1095,1000., 950, 9430, 815, 795, 725, 690 cm⁻¹. UV nm ζ: 207 (2.5×10³). Anal.Calc. for C₈ H₁₂ Si: C, 70.51; H, 8.88. Found: C, 70.96; H, 9.06.

EXAMPLE 4 Poly(1-Phenyl-1-vinyl-1-sila-cis-pent-3-ene) (I)

In a 100 mL rb flask equipped with a Teflon covered magnetic stirringbar and rubber septum was placed 1-phenyl-1-vinyl-1-silacyclopent-3-ene(1.00 g, 5.4 mmol), THF (40 mL) and HMPA (40 μL). The mixture was cooledto -78° C. and a hexane solution of N-butyllithium (80 μL, 2.5M, 0.2mmol) was added via a syringe. The reaction mixture was stirred at -78°C. for 1 h. A saturated solution of aqueous ammonium chloride (15 mL)was added. The organic layer was separated, washed with water (20 mL),dried over anhydrous magnesium sulfate, filtered and the volatilesolvents removed by evaporation under reduced pressure. The residue wasdissolved in a minimum amount of THF and (I) was precipitated frommethanol. This process was repeated twice. (I) was dried under vacuum.In this way, 0.80 g, 80% yield of (I), M_(w) /M_(n) =10,400/6,800 wasobtained. ¹ H NMR s: 0.89 (br,s,0.16H), 1.34 (br,s,0.16H), 1.51(br,s,0.15H), 1.71 (d,4H,J=5.4 Hz), 5.35 (t,2H,J=5.4 Hz), 5.77(d,d,1H,J=20 Hz,J=3 Hz), 6.11 (d,d,1H,J=14.5 Hz, J=3.7 Hz), 6.23(d,d,1H,J=20 Hz, J=14.5 Hz), 7.34 (m,3H), 7.46 (m,2H). ¹³ C NMR δ:13.77, 127.64, 129.17, 134.50, 134.59, 134.80, 135.71. ²⁹ Si NMR δ:-13.24. IR ν: 3069, 3051, 3020, 2968, 2945, 2916, 2890, 1609, 1592,1429, 1404, 1235, 1204, 1172, 1115, 1100, 1007, 956, 945, 878, 817, 802,726, 698, 638, 618 cm⁻¹. UVλ_(max) nm(ζ) (ether) 216 (18,500). Anal.Calc. for C₁₂ H₁₄ Si: C, 77.39; H, 7.58. Found: C, 76.53; H, 7.83.

EXAMPLE 5 Copolymer of poly(1-Phenyl-1-vinyl-1-sila-cis-pent-3-ene) andpoly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene (III)

In a 100 mL rb flask equipped with a Teflon covered magnetic stirringbar and rubber septum were placed 1-phenyl-1-vinyl-1-silacyclopent-3-ene(0.50 g, 2.7 mmol) and 1-methyl-1-phenyl-1-silacyclopent-3-ene (0.50 g,2.9 mmol), THF (40 mL) and HMPA (40 μL). The mixture was cooled to -78°C. and a hexane solution of N-butyllithium (80 μL, 2.5M, 0.2 mmol) wasadded via a syringe. The reaction mixture was stirred at -78° C. for 1h. A saturated solution of aqueous ammonium chloride (15 mL) was added.The organic layer was separated, washed with water (20 mL), dried overanhydrous magnesium sulfate, filtered and the volatile solvents removedby evaporation under reduced pressure. The residue was dissolved in aminimum amount of THF and (III) was precipitated from methanol. Thisprocess was repeated twice. (III) was dried under vacuum. In this way,0.78 g, 78% yield of (III), M_(w) /M_(n) =13,000/8,800 was obtained. ¹ HNMR δ: 0.25(s,1.7H), 1.63(m,2.2H), 1.72(m,1.8H), 5.33 (m,2H), 5.78(d,d,0.45H, J=20 Hz, J=4 Hz), 6.11(d,d,0.45H, J=14.8 Hz, J=4 Hz), 6.24(d,d,0.45H, J=20 Hz, J=14.8 Hz), 7.33(m,3H), 7.49(m,2H), ¹³ C NMR δ:-5.49, 13.63, 1376, 15.22, 122.79, 123.24, 123.69, 127.62, 128.95,129.14, 133.82, 134.39, 134.58, 134.81, 135.72, 137.75. ²⁹ Si NMR δ:-13.32, -13.29, -13.25, -4.40, -4.35, -4.30. IR ν: 3069, 3049, 3009,2955, 2924, 2886, 1638, 1428, 1404, 1376, 1250, 1152, 1113, 1027, 998,954, 930, 787, 732, 699, 618 cm⁻¹. UVλ_(max) nm (ζ)(ether)216(25,040).

EXAMPLE 6 Crosslinking of poly(1-phenyl-1-vinyl-1-sila-cis-pent-3-ene)with 1,1,10,10-tetramethyl-1,10-disiladecane

0.0575 g 1-phenyl-1-vinyl-1-silacyclopent-3-ene, 0.0354 g,1,1,10,10-tetramethyl-1,10-disiladecane, and 0.0023 g diluted PC075platinum (0.3 wt % Pt) complex (Huls America) were mixed and placed on aceramic mounted sensor in a Dupont Dielectric Analyzer. The dielectricconstant and dissipation factor of the sample before curing was 3.03 and0.0877 (1 KHz). The sample was heated to 110° C. for 4 hours and cooledunder nitrogen to 30° C. to give a cured polymer dielectric constant (E2.18) and dissipation factor (DF 0.0044).

EXAMPLE 7 Crosslinking of the Copolymer ofPoly(1-phenyl-1-vinyl-1-sila-cis-pent-3-ene) andPoly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) with1,1,10,10-tetramethyl-1,10-disiladecane

0.0869 g of the copolymer above, 0.0247 g1,1,10,10-tetramethyl-1,10-disiladecane, and 0.0010 g diluted (0.3 wt %Pt) PC075 platinum complex (Huls America) were mixed and placed on aceramic mounted sensor in a Dupont Dielectric analyzer. The dielectricconstant and dissipation factor of the sample before curing was 2.27 and0.0785 at 1 KH_(z). After curing at 110° C. for 4 hours and cooling to30° C. under nitrogen the dielectric constant and dissipation factor ofthe cured resin was E 2.23 DF 0.0055. After curing up to 200° C. (2 hrat 200° C.) under N₂, the dielectric constant was 2.27 and thedissipation factor was 0.0085.

EXAMPLE 8 1-phenyl-1-vinyl-1-silacyclobutane

A dry 250 ml three neck round bottom flask equipped with a droppingfunnel and condenser with nitrogen inlet system. Was placed 4.2 g (23mmole) 1-chloro-1-phenyl-1-silacyclobutane in 40 ml THF. With stirring,25 ml (0.1M) vinyl magnesium bromide (in THF) was added dropwise. Themixture was stirred for additional 6 h. Work up, the mixture wasdistilled to collect 2.8 g 82°-83° C./3.0 mmHg 70% yield was obtained.

EXAMPLE 9 Poly(1-phenyl-1-vinyl-1-silabutane)

In a 100 mL rb flask equipped with a Teflon covered magnetic stirringbar and rubber septum was placed 1-phenyl-1-vinyl-1-silacyclobutane(1.00 g, 5.4 mmol), THF (40 mL) and HMPA (40 μL). The mixture was cooledto -78° C. and a hexane solution of n-butyllithium (80 μL, 2.5M, 0.2mmol) was added via a syringe. The reaction mixture was stirred at -78°C. for 1 h. A saturated solution of aqueous ammonium chloride (15 mL)was added. The organic layer was separated, washed with water (20 mL),dried over anhydrous magnesium sulfate, filtered and the volatilesolvents removed by evaporation under reduced pressure. The residue wasdissolved in a minimum amount of THF andpoly(1-phenyl-1-vinyl-1-silabutane) was precipitated from methanol. Thisprocess was repeated twice. The polymer was dried under vacuum. In thisway, 0.63 g, 63% of polymer was obtained, M_(w) /M_(n) =15,800/11,300was obtained. Tg= -18. ¹ H NMR (δ) 0.845 (m. 4H), 1.370 (m. 2H), 5.850(m. 1H), 6.012 (m. 1H), 6.147 (m. 1H), 7.296 (m. 3H), 7.378 (m. 2H). ¹³C NMR (δ) 127.64, 128.82, 133.76, 134.37, 135.76, 136.60. ²⁹ Si NMR (δ)-10.86. IR (ν) 3135, 3068, 3048, 3009, 2919, 2875, 2793, 1653, 1591,1487, 1456, 1427, 1403, 1336, 1302, 1261, 1235, 1216, 1191, 1140, 1110,952, 900, 790, 699. UV λmax nm(ζ) 271 (913), 266 (1680), 260 (1933), 254(1267), 230 (9667). C₁₁ H₁₄ Si Calc. C; 75.68, H; 8.28. Found. C; 75.83,H; 8.10.

EXAMPLE 10 Crosslinking of Poly(1-phenyl-1-vinyl-1-silabutane) and1,1,10,10-tetramethyl-1,10-disiladecane

0.0890 g poly(1-phenyl-1-vinyl-1-silabutane), 0.0588 g,1,1,10,10-tetramethyl-1,10-disiladecane and 0.0022 g diluted (0.3% Pt)PC075 platinum catalyst (Huls America Inc.) were mixed and placed on aceramic mounted sensor in a Dupont Dielectric Analyzer. The sample washeated at 110° C. for four hours and then cooled to 30° C. undernitrogen. The dielectric constant of the cured sample was 2.29 (1KH_(z)) and the dissipation factor was 0.0029.

We claim:
 1. A poly(unsaturated carbosilane) comprising a plurality ofrepeating units of the formula ##STR6## wherein R is vinyl, alkylcontaining one to four carbon atoms or phenyl;R₁ is hydrogen, alkylcontaining one to four carbon atoms, phenyl, or halogen; and R₂ ishydrogen or R₁ and R₂ together with the adjacent carbon atoms of eachform a phenyl ring.
 2. A poly(unsaturated carbosilane) polymer asclaimed in claim 1 wherein R is vinyl and R₁ and R₂ are each hydrogen.3. A poly(unsaturated carbosilane) polymer as claimed in claim 1 whereinR is methyl and R₁ and R₂ are each hydrogen.
 4. A poly(unsaturatedcarbosilane) polymer as claimed in claim 1 wherein R is phenyl and R₁and R₂ are each hydrogen.
 5. A poly(unsaturated carbosilane) polymer asclaimed in claim 1 wherein R is methyl and R₁ and R₂ together are aphenyl ring.
 6. A poly(unsaturated carbosilane) polymer as claimed inclaim 1 wherein R is phenyl and R₁ and R₂ together are a phenyl ring. 7.A polycarbosilane comprising a plurality of repeating units of theformula ##STR7## wherein R is vinyl, alkyl containing one to four carbonatoms or phenyl, R₁ is hydrogen, alkyl containing one to four carbonatoms, phenyl or halogen, and R₃ is hydrogen, alkyl containing one tofour carbon atoms or phenyl.
 8. A polycarbosilane as claimed in claim 7where R is methyl and R₁ and R₂ are hydrogen.
 9. A polycarbosilane asclaimed in claim 7 where R is phenyl and R₁ and R₂ are hydrogen.
 10. Apolycarbosilane as claimed in claim 7 where R is methyl and R₁ ismethyl.
 11. A polycarbosilane as claimed in claim 7 where R is phenyland R₁ is methyl.
 12. A polycarbosilane as claimed in claim 7 where R isvinyl.
 13. A method for preparing the poly(unsaturated carbosilane)claimed in claim 1 which comprises polymerizing monomers of the formula##STR8## wherein R, R₁ and R₂ are as defined in claim 1, in the presenceof an anionic ring opening catalyst system.
 14. The method as claimed inclaim 13 wherein the anionic ring opening catalyst system is anorganometallic base and cation coordinating ligand catalyst system. 15.A method for preparing a polycarbosilane claimed in claim 7 whichcomprises polymerizing monomers of the formula ##STR9## wherein R, R₁and R₃ are defined in claim 7, in the presence of an anionic ringopening catalyst system.
 16. The method claimed in claim 15 wherein theanionic ring opening catalyst system is an organometallic base andcation coordinating ligand catalyst system.